Integral electrical coil structure

ABSTRACT

An integral, cast electric coil structure includes an open mesh supporting spool with at least one coil of electrical conductor supported on the spool and an encapsulant substantially encasing the spool and the coil. Portions of the encapsulant are both inside and outside of the spool and extend through openings in the spool to form an integral structure.

o I United States Patent 1 1 3,737,823 Mees et al. a [451 June 5, 1973 s41 INTEGRAL ELECTRICAL COI L 3,030,597 4/1962 Piaia, Jr. et al. ..336/96 x STRUCTURE 3,041,562 6/1962 3,662,461 /1972 [75] Inventors: Robert D. Mees, Fort Wayne, lnd.; 3,348,302 10/1967 George I. Duncan, Danville, 111. 1,239,003 9/1917 3 3,377,602 4/1968 Kruse ..336/205 X [73] Assignee: General Electric Company, Fort Wayne, Primary Examiner-Thomas .l. l(ozma Attorney-John M. Stou t, Ralph E. Kirshner, Jr., 22 Fl D 17 71 r l 1 led cc 19 Robert B. Kennedy et al. 3 [21] Appl. No.: 209,193 [57] ABSTRACT An integral, cast electric coil structure includes an v 336/203 open mesh supporting spool with at least one coil of [51] Int. Cl. ..H01f 27/30 electrical conductor supported on the spool and an [58] Field of Search ..336/96, 205, 198, encapsulant substantially encasing the spool and the 336/208, 192 coil. Portions of the encapsulant are both inside and outside of the spool and extend through openings in [56] References Cited the spool to form an integral structure.

UNITED STATES PATENTS 13 Claims, 5 Drawing Figures 3,396,356 8/1968 Whipple ..336/205 x |33 N I 34 ll3 12 I I 16 "4O 35w;

1 I r23 37 3: 1'16 3Q J I 2G Patented Jl me 5, 1973 v 3,737,823

2 Shoezs-Sheet 1 vain mi 43 Patented Ju'm 5,1913

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1 INTEGRAL ELECTRICAL COIL STRUCTURE BACKGROUNDOF THEINVE'NTION This invention relates' generally to an improved integral electrical coil structureand more particularlyto an electrical coil structure ofthe cast type wherein the electrical conductors are encased in an encapsulant material. Such coil structures are particularly useful in electrical transformerapplications. his highly desirable that as much as possible of thevapor ge'nerated during the coil forming-operation be eliminated from thefinal cast structure and that the encapsulantform a solid covering, whichwill-remainsolid during'operation to preclude entryof contaminants'such asmoisture. If an appreciable amount of vapor is trapped in the coil structure during the encapsulating process voids will be formed in the encapsulant which ca'nlead to coronadegradation of the coil system. Cracks'or other openings which may form in the finalstructure can-allow such contaminants suchas moisture to enter the coil structure and cause malfunction'of the coil.

In the past electric coils of this-general type have been formed using a solid bobbin.With such'*coil structures a bobbin in the form of a solid-cylindrical wallis formed, normally by casting a suitable material such as a resin. Individual coils of "electric conductor are then mounted on the bobbin; the bobbin is (placed in a mold; and an encapsulant material is cast aroundthe coils. Withsuch an approach ,thebobbinform's the radially inner wall of the mold and is notencased inthe encapsula'ntxT his requires thatthe encapsulant-firmly adhere to the wall of the bobbin and coils-constructed in this manner on a occasion failbecause. the encapsulant and bobbin part. Additionally, since vapors cannot move through the solid wall of the bobbin, excessive amounts of vapor tend to be captured within the encapsulant, particularly adjacent the coils.

Accordingly, as an object of the..presentinvention to provide a new and improved integral electric'coil struc- SUMMARY OF THE INVENTION According to one form of the present invention there may be-formed from elongated glass fibers coated with a suitable epoxy resin.

The subject matter which we regard as our invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention itself; however, together with further objects and advantages thereof, best may be understood by reference to the following description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS rial, and with the uppersection of the mold removed for purposes of illustration;

FIG. 4 is a somewhat schematic cross-sectional view of a complete mold with spool and coils mounted therein, the view beinggenerally as would be seen along line 4- -4 of FIG. 3, and with part of the coil and supporting spool broken away for purposes of illustration; and

FIG. 5 is a block diagram flow chart illustrating the basic steps utilized in making the exemplification coil structure of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1 there is shown an integral electric coil structure 10 having a generally hollow cylindrical main body 11, which encases a number of electrical coils, a pair of outwardly extending and somewhat divergent arms 12, which encase terminations or terminals 13 for leads to the coils. Such an integral electric coil structures in which one or more coils are encased by suitable encapsulant may advantageously be used in electrictransformers of various sizes of and ratings. By way of example such-coil structures may have an inner diameter of about 15 inches, an outer diameter of 18 inches, height or length of about 36 inches and may weigh several hundred-pounds. The relatively large sizes that these structures mayassume increases the problems of obtaining good permanent encapsulation of the coils with minimum trapping of vapor.

Such "coil structures normally include one or more coils." Each of the coils includes a number of turns and an electrical conductor wound in layers with suitable insulation provided between the layers. Each of the individual coils is separated from the other coils'and all of the coils are encased in a body of encapsulating material which serves to support the coils, protect them from the elements and conduct heat away from them. ldeally it would be desirable to have the coils freely suspended in a body of encapsulating material. However, since the encapsulating materialis cast about the coils in a essentially liquid state and then cured, the coils must be supported within the encapsulating material. Use of any support which is removed after the encapsulant cures would prevent the encapsulant from forming a solid body around the coils.

We have found that by mounting the coils on a selfsupporting open mesh spool and then casting a body of encapsulating material around both the open mesh spool and the coils, with the encapsulating material on the inside and the outside of the spool joining through openings in the spool, there is provided a integrated electric coil structure in which the encapsulating material forms an essentially solid mass around the coils. Such a structure also provides enhanced egress of vapor during the casting process to at least greatly reduce, if not eliminate, creation of voids within the cast structure.

Referring particularly to FIGS. 3 and 4 there is illustrated an open mesh spool and six individual coils 16 which form a spool and coil subassembly of the exemplification coil structure 10. It will be noted that the spool 15 includes a central or main body portion 17 of a crossed strip of material defining a plurality of generally diamond shaped openings 19 and a pair of spaced apart, substantially solid end portions 18. The coils 16, each of which conventionally may be a plurality of turns of an electrical conductor, are supported on the main body portion 17 so that openings 19 are provided between the individual coils. Since the spool 15 must support the coils during the manufacturing process, at least until the encapsulant is cured, the spool should be self-supporting and capable of supporting the individual coils, both when the spool is in a vertical position and when the spool is in a horizontal position. An integral, open mesh, wound spool particularly suitable for use in the present invention, as well as an apparatus for forming such a spool is shown and described in copending application Ser. No. 209,182 filed concurrently herewith and assigned to General Electric Co., assignee of the present invention.

Leads 20 extend from the various coils and are connected to the terminals 13 which conveniently are placed in at least a pair of angularly separated positions relative to the coils for assisting in making proper connections to the coils.

In order to encase the spool and coils a mold is provided and includes two separate mating mold halves 26 and 27, which are joined to form the complete mold. The assembled mold provides a radially inner wall 28, which is spaced inwardly from the spool 15 and a radially outer wall 29, which is spaced outwardly from the outer circumference of the coils 16. The inner and outer walls are joined by end walls 30, which are spaced beyond the ends of the spool 15. The walls 28, 29 and 30 define a mold cavity 31. The spool and coils are supported within the mold cavity in spaced relationship to each of the walls so that the encapsulating material will completely surround the spool and the coils. In order to properly position the spool and coils within the mold cavity 31, the end walls of the mold are provided with slotted pins, such as those shown in 32, which engage the end portions 18 of the spool. While only two such pins are shown, conveniently three or more pins may be provided in each end wall so as to as-. sure proper positioning of the spool, and thus the coils, regardless of the orientation of the mold. The number of pins is kept to a minimum consistent with proper positioning of the spool so as to provide as few discontinuities in the encapsulant as possible.

The outer wall 29 of the mold is provided with a pair of outwardly extending recesses 33 which provide the arms 12 for receiving the terminals 13. The outer edges of the wall 29 are open adjacent the recesses 33. In assembling the mold about a spool and coil subassembly the terminals 13 are attached to plates 34 by means of bolts 35 which extend through the plates and are received in the terminals. The plates 34 are then mounted against the outer wall 29 of the mold by means of U shaped clips 36 which are received in slots in the mold wall 29 and overlap the plates 34. In order to assure a tight fit between the clips, the plates and the mold wall, gaskets 37 are provided between each of the clips in the adjacent plate. The plates 34 close the open ends of the recesses 33 and properly position the terminals 13 during the molding or casting process.

Generally opposite the recesses 33, the mold outer wall 29 is provided with an opening 40 which is surrounded by a flange 41. Once the spool and coil subassembly has been mounted in the mold, the mold is turned to a position so that the opening 40 is up and a suitable encapsulant material is poured into the mold through the opening 40. The flanges 41 provide a reservoir to receive additional encapsulant material. The encapsulant normally shrinks during the curing process and the reservoir provides additional encapsulant material which assures that the mold remains full during curing.

The encapsulant normally will be a somewhat viscous fluid when poured into the mold. By supporting the spool and coil subassembly a spaced relationship to the walls defining the mold cavity 31, the liquid encapsulating material will be free to flow completely around the spool and the coils as it fills the mold cavity. The openings 19 in the spool between coils allow the portion of the encapsulant material radially inside the spool and the portion radially outside the spool to be joined together to form an integral structure. Furthermore, the openings 19 in register with the coils l6 allow the encapsulant material to come into intimate contact with the radially inner-portions of the coils. The openings 19 also provide freedom for escape of vapors, which are generally formed adjacent the spool or coil during the curing process, and better allows for escape of air which may be trapped during the encapsulant pouring step. Thus, when the encapsulant cures the encapsulated structure is essentially free of voids or trapped vapor and the body of encapsulating material essentially completely encases the spool, the coils and the terminations. ,The pins 32 are so sized and the axially outer coils are so positioned on the spools that the recesses in the body of encapsulating material formed by the pins 32 do not extend to the coils. After the encapsulant material has cured the coil structure is removed from the mold and the small indentations in the encapsulant left by the pins 32 are filled with a suitable material.

The integral nature of the coil structure is best illustrated in fragmentary view of FIG. 2. In that figure it will be seeri that the crossed strip main body portion 17 of the spool supports a coil 16 in a body 42 of encapsulating material. A-first portion 43 of the body of encapsulating material is radially outside the spool and ex tends around and completely encases the coil 16. A second portion 44 of the body of encapsulating material is radially inside the spool and the two portions of the encapsulating material are joined through the openings 19 between the strips of material forming the spool. Also it will be seen from FIG. 2 that the electrical coils 16 may include anumber of layers of electrical conductor 45, with each layer being separated from other layers by a sheet 46 of an insulating material such as paper. For ease of illustration the wire 45 has been shown schematically in an uninsulated state. However, it will be recognized that normally the wire itself is insulated so the individual turns are insulated from each other. Alsoit will be understood that coils.l6 often are wound from flat wire.

The spool, the coil and the encapsulatingmaterial should be compatible. Additionally the spool should be a self-supporting structure capable of also supportingthe coils until the encapsulating material has hardened. Additionally the encapsulating material should be essentially impervious to the atmosphere inwhichthe electrical apparatus in which it is used and should conduct heat away from the coils without adverse effect on the encapsulating material.

Byway of example, the spool may be formed by winding an elongated strip of glass fibers coated with epichlorohydrin-bisphenol-A epoxy resinwith twoethyl-four-methyl imidaz ole as an accelerator. When the spool is constructed of such a material the encapsulant advantageouslymay consist of epichlorohydrim bisphenol-A epoxy resin. with phthalic anhydride as a crosslinking agent and may have a filler of silicon dioxide. vOne encapsulant mixture particularly suited for this use has one hundred partsbyweight of resin to two hundred parts by weight of silicon dioxide-having an average size of about 300 and 25 (325) mesh; The silicon dioxide filler increases. the strength and the heat dissipating properties of the encapsulant material. It willbe understood that'the other encapsulating materials could be used. For instance the encapsulating material could be a cycloaliphatic epoxy, a glycol modified epoxy or a polyester resin, any of which may have a particulate filler.

An integral, cast electric coil structure generally as described above, has a number of advantages. This is particularly true wherethe spool is of anopen mesh configuration wound of epoxy coated glass fibre. Magnetic andIelectrical properties of transformer design often dictate that the volume ofthe second or inner portion 44 of the body of encapsulant material be held small. The epoxy-glassfspool reinforces this portion of the encapsulant and reduces anytend'ency of it to crack. Alsothe volume of inner portion 44 often is small as compared to the first or outer portion 43. Such a difference in volume tends to cause stresses to be built up in the encapsulant material, both as result of differences in the curing, times of these portions and as a result of thermal shocks to which the coil structure later may be subjected. Theepoxy-glass-open mesh spool compensates for such stresses and greatly reduces the tendency of the encapsulant to crack as a result of such stresses. All of these factors tend to improve the electrical capability of the cast coil structure.

Generally as illustrated'in FIG-5 the integral electric coil structure of the exemplification is formed by a process in which first the spool is formed or wound. The coating resin of the, spool then is cured as by heating the spool in an oven. Thereafter the individual c'oilsl6 are mounted onthe spool -15. These coils may.be-preformed and then mounted on the spool; however, it is desirable that the coils b'e wound directly on the spool.

One advantage of the self-supporting spool structure of the aforementioned copending application is that, with appropriate support during the winding process it will withstand the forces developed by winding the coils directly on the spool.

Thereafter the spool and coil subassembly is impregnated with a suitable material such as epichlorohydrinbisphenol-A and an organo-metal catalyst system with methyl-nadic anhyride cross-linking agent. The impregnant is cured by heating the impregnated subassembly in a suitable oven, as is well known in the art. The purpose of impregnating the spool and the coil subassembly isthat the impregnant material tends to fill any as to drive out unwanted vapors and provide a better overall structure. Since the coils 16 are mounted over the main body portion 17 of spool 15, impregnant material can reach the inner portions of the coils 16. This provides much improved impregnation of the coils. Thereafter the spool and coil subassembly is mounted in the mold and the mold is filled with a suitable encapsulating material, which is then cured. This cure may be enhanced by heating in a suitable oven, again is as well known in the art.

While we have described what we presently consider the preferred embodiments of the'invention, it will be understood that various modifications may be made therein without departing from the invention. Therefore it is aimed in the appended claims to cover all such modifications as fall within the true spirit and scope of the invention.

What we claim as new and desire to secure by Letters Patent in, the United States is:

L'An electric coil structure, including:

a. an open mesh, self-supporting spool;

b. at least one coil of electrical conductor supported said spool with said open mesh spool extending axially beyond said at least one coil; and

c. an encapsulant substantially encasing said spool and said coil;

d. said encapsulant filling the openings in said spool for forming an integral structure.

2. An electric coil structure as set forth in claim 1 wherein; said spool is generally cylindrical in form; said encapsulant including a first, solid portion radially inwardly of said spool and a second, solid portion radially outwardly of said spool; said first and second portions of said encapsulant being joined through openings in said spool.

3. An electric coil structure as set forth in claim 1 wherein: said encapsulant is a cast resin material having a particulate filler.

4. An electric coil structure as set forth in claim 3 wherein; said encapsulant includes about parts by weight of epichlorohydrin-bisphenol-A epoxy resin with phthalic anhydride as a crosslinking agent and about 200 parts by weight of silicon dioxide filler.

5. An electric coil structure as set forth in claim 4 wherein: said spool and said at least one coil of electrical conductor are impregnated with epichlorohydrinbisphenol-A epoxy resin and an organo-metal catalyst system with methyl-nadic anhydride as a crosslinking agent.

6. An electric coil structure as set forth in claim 2: wherein at least one termination for said at least one coil is formed radially of said at least one coil; said encapsulant including at least one radial portion substantially encasing said at least one termination.

7. An electric coil structure, including:

a. a self-supporting spool having a generally cylindrical body section, defining a plurality of openings therein, and a pair of solid, ring like end sections formed integrally with said body sections;

b. at least one coil, including a plurality of turns of electrical conductor, supported on said body section of said spool with said body section extending axially beyond said at least one coil;

c. an encapsulant substantially encasing said spool and said at least one coil;

d. said encapsulant including a first, solid portion, radially inward of said spool, and a second, solid portion radially outward of said spool; said first and second portions of said encapsulant being joined through openings in said body portion of said spool to form an integral structure.

8. An electric coil structure as set forth in claim 7; wherein there are a plurality of coils axially spaced apart along said body section of said spool; said encapsulant substantially filling the space between adjacent pairs of coils so as to substantially encase each of said 8 coils.

9. An electric coil structure as set forth in claim 7 wherein: said spool is a self-supporting member composed of an essentially continuous strip of filamentary material coated with a cured resin.

10. An electric coil structure as set forth in claim 7 wherein: said spool is a self-supporting member composed of essentially continuous glass fiber coated with epichlorohydrin-bisphenol-A epoxy resin and twoethyl-four-methyl imidazole as an accelerator.

11. An electric coil structure as set forth in claim 10 wherein: said spool and said at least one coil are impregnated with epichlorohydrin-bisphenol-A epoxy resin and an organo-metal catalyst system with methylnadic anhydride as a crosslinking agent.

12. An electric coil structure as set forth in claim 10 wherein: said encapsulant includes epichlorohydrinbisphenol-A epoxy resin with phthalic anhydride as a crosslinking agent and silicon dioxide filler.

13. An electric coil structure as set forth in claim 7 wherein: said encapsulant is a cast resin material having a particulate filler. 

1. An electric coil structure, including: a. an open mesh, self-supporting spool; b. at least one coil of electrical conductor supported said spool with said open mesh spool extending axially beyond said at least one coil; and c. an encapsulant substantially encasing said spool and said coil; d. said encapsulant filling the openings in said spool for forming an integral structure.
 2. An electric coil structure as set forth in claim 1 wherein; said spool is generally cylindrical in form; said encapsulant including a first, solid portion radially inwardly of said spool and a second, solid portion radially outwardly of said spool; said first and second portions of said encapsulant being joined through openings in said spool.
 3. An electric coil structure as set forth in claim 1 wherein: said encapsulant is a cast resin material having a particulate filler.
 4. An electric coil structure as set forth in claim 3 wherein; said encapsulant includes about 100 parts by weight of epichlorohydrin-bisphenol-A epoxy resin with phthalic anhydride as a crosslinking agent and about 200 parts by weight of silicon dioxide filler.
 5. An electric coil structure as set forth in claim 4 wherein: said spool and said at least one coil of electrical conductor are impregnated with epichlorohydrin-bisphenol-A epoxy resin and an organo-metal catalyst system with methyl-nadic anhydride as a crosslinking agent.
 6. An electric coil structure as set forth in claim 2: wherein at least one termination for said at least one coil is formed radially of said at least one coil; said encapsulant including at least one radial portion substantially encasing said at least one termination.
 7. An electric coil structure, including: a. a self-supporting spool having a generally cylindrical body section, defining a plurality of openings therein, and a pair of solid, ring like end sections formed integrally with said body sections; b. at least one coil, including a plurality of turns of electrical conductor, supported on said body section of said spool with said body section extending axially beyond said at least one coil; c. an encapsulant substantially encasing said spool and said at least one coil; d. said encapsulant including a first, solid portion, radially inward of said spool, and a second, solid portion radially outward of said spool; said first and second portions of said encapsulant being joined through openings in said body portion of said spool to form an integral structure.
 8. An electric coil structure as set forth in claim 7; wherein there are a plurality of coils axially spaced apart along said body section of said spool; said encapsulant substantially filling the space between adjacent pairs of coils so as to substantially encase each of said coils.
 9. An electric coil structure as set forth in claim 7 wherein: said spool is a self-supporting member composed of an essentially continuous strip of filamentary material coated with a cured resin.
 10. An electric coil structure as set forth in claim 7 wherein: said spool is a self-supporting member composed of essentially continuous glass fiber coated with epichlorohydrin-bisphenol-A epoxy resin and two-ethyl-four-methyl imidazole as an accelerator.
 11. An electric coil structure as set forth in claim 10 wherein: said spool and said at least one coil are impregnated with epichlorohydrin-bisphenol-A epoxy resin and an organo-metal catalyst system with methyl-nadic anhydride as a crosslinking agent.
 12. An electric coil structure as set forth in claim 10 wherein: said encapsulant includes epichlorohydrin-bisphenol-A epoxy resin with phthalic anhydride as a crosslinking agent and silicon dioxide filler.
 13. An electric coil structure as set forth in claim 7 wherein: said encapsulant is a cast resin material having a particulate filler. 